The photo on the cover of retired Secret Service agent Clint Hill’s memoir of guarding Jacqueline Kennedy is telling. Hill is hanging his head, and Jackie seems just about to offer a reassuring word.

It was Hill who leapt onto the presidential limousine in Dallas to shield the Kennedys as the fatal shots were fired. “And then came the thought that haunts me still,” he writes. “How did I let this happen to her?”

The story told in Mrs. Kennedy and Me offers many happier moments Hill shared with Jackie: tales of international travel, quiet rides through the Virginia countryside, even a playful challenge to Hill from the experienced First Lady to try water skiing.

What emerges is a portrait of a lady, someone used to privilege but also comfortable mocking its strictures. This must have made her attractive to her similarly-inclined husband.

Hill matches his dismay at being consigned to the First Lady’s security detail in 1960 to her own discomfort at having agents monitor her every move. From that awkward beginning, they forged a working relationship that grows into a friendship.

Mrs. Kennedy and Me offers a fine selection of formal and informal photos ranging from grand state dinners to a classic of Jackie taking a header after a photographer startled her horse. Another, showing her water-skiing with 4-year-old Caroline, caused much public clucking about child endangerment.

On June 30, 1961, Hill and his fellow agents arrived at the Summer White House in “sleepy” Hyannis Port. With a “twelve-dollar per diem,” they “all chipped in on food and other necessary items…” Things looked up when the president brought them cartons of chowder from Mildred’s.

By 1963, Hill was at home in “quaint and unpretentious” Hyannis Port, even to the point of running out to Lorania’s Toy & Book Shop downtown for candy and toys for the children. It was an idyllic time in which the agent accompanied the First Lady on her walks from Squaw Island to Ambassador Kennedy’s house for long visits with the president’s father.

But this was also the summer in which baby Patrick was born and struggled briefly for life. In the wake of the tragedy, Hill and his fellow agents noticed “a distinctly closer relationship, openly expressed, between the president and Mrs. Kennedy.” After a refreshing overseas trip, Jackie told Hill that she felt well enough to accept Jack’s offer to join him on a campaign trip to Texas.

As a sort of knight-in-waiting at Camelot, Hill witnessed the backstage life the rest of us only imagined. He is discreet but generous in sharing what he saw, both the joy and pain. At the end of the book, he draws a final veil over those years:

“We had been through so much together, Mrs. Kennedy and me. More than anyone can imagine.

“More than anyone can ever know.”

Clint Hill will speak in Fellowship Hall at Federated Church of Hyannis on Main Street July 15 at 4 p.m. as part of the JFK Hyannis Museum lecture series. A book signing will follow at the museum. Admission to the talk is free, but reservations are required; go to www.jfkhyannismuseum.org.